Organic light emitting devices (OLEDs) can suffer reduced output or premature failure when exposed to water vapor or oxygen. Metals and glasses have been used to encapsulate and prolong the life of OLED devices, but metals typically lack transparency and glass lacks flexibility. Intense efforts are underway to find alternative encapsulation materials for OLEDs and other electronic devices. Examples include various types of vacuum processes are described in the patent and technical literature for the formation of barrier coatings. These methods span the range of e-beam evaporation, thermal evaporation, electron-cyclotron resonance plasma-enhanced chemical vapor deposition (PECVD), magnetically enhanced PECVD, reactive sputtering, and others. Barrier performance of the coatings deposited by these methods typically results in a moisture vapor transmission rate (MVTR) in the range from 0.1-5 g/m2 day, depending on the specific processes. Graff (WO0036665) demonstrates the importance of separating multiple inorganic oxide coatings with vapor deposited highly cross-linked polymer layers to achieve barrier performance necessary for OLED device substrates.
It is commonly accepted that multiple inorganic layers separated by polymer coatings are needed to achieve superior barrier performance. U.S. Pat. No. 5,320,875 teaches the importance of a plasma polymerized siloxane monomer and an adhesion promoter in addition to generating the plasma in an “oxygen excessive” mode and depositing the coatings in the “plasma reaction zone” to obtain improved barrier performance. The best barrier coatings made by this process still have an MVTR of 0.23 g/m2 day. Da Silva Sobrinho et al. (Surface and Coatings Technology, 116-119, p 1204, 1999) report a microwave and radio frequency combined process for depositing barrier coatings. In U.S. Pat. No. 6,146,225, Sheats et al. claim that a high density plasma with low bias voltage results in superior quality barrier coatings.
References relating to flexible barrier films include U.S. Pat. No. 5,440,446 (Shaw et. al.), U.S. Pat. No. 5,530,581 (Cogan), U.S. Pat. No. 5,681,666 (Treger et al.), U.S. Pat. No. 5,686,360 (Harvey, III et al.), U.S. Pat. No. 5,736,207 (Walther et al.), U.S. Pat. No. 6,004,660 (Topolski et al.), U.S. Pat. No. 6,083,628 (Yializis), U.S. Pat. No. 6,146,225 (Sheats et al.), U.S. Pat. No. 6,214,422 (Yializis), U.S. Pat. No. 6,268,695 (Affinito), U.S. Pat. No. 6,358,570 (Affinito), U.S. Pat. No. 6,413,645 (Graff et al.), U.S. Pat. No. 6,492,026 (Graff et al.), U.S. Pat. No. 6,497,598 (Affinito), U.S. Pat. No. 6,497,598 (Affinito), U.S. Pat. No. 6,623,861 (Martin et al.), U.S. Pat. No. 6,570,325 (Graff et al.), U.S. Pat. No. 5,757,126, U.S. Patent Application No. 2002/0125822 A1 (Graff et al.), and PCT Published Application No. WO 97/16053 (Robert Bosch GmbH).